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All Calculations relating to the action of the Slide Valve, no matter how intricate, can he solved in a few moments by the use of the Calculator 
The information it gives is read off at sight, and is at once intelligible and correct. 

By a short examination the following points can be ascertained by a person ot common attainments, every point proving itself as the examin 
ation progresses. 



1. The proper travel of Valve to produce certain results. 

2. The proper Lap to Cut off at given part of stroke. 

3. " " Exhaust " " " 

4. " " Cushion " " " 

5. " " Cut off equal on each side of Piston. 

6. " " Exhaust " " " " 

7. " " Cushion " " " " 



The proper width of Exhaust port to prevent back pressure. 
The proper Lead to give the Valve. 
The proper amount of opening for admission of Steam. 
The position of ' • ntric on Shaft. 

The relation of ^' ' e to Piston at every part of the stroke. 
These points ascertained at sight with Lead or without it. 



[COPY BIGHT BY JOHN A. CALDWELL, mi.] 



■isMaHeaerr- 







DIRECTIONS FOR USING 



SLIDE yALTE CALCULATOR. 



Cut paper Template, ( See fig. 1,) the large circle repre- 
senting the stroke of engine, eighth size, and the small 
circle the travel of the valve, full size. ^ For an engine 24 
in. stroke and 2 in. travel of valve, these circles would be 
respectively, 3 in. and 2 in. 




Fia. 1. 

Place the Calculator before us so that tlie letters B. and 
F. will read from left to right. Place the Template on 
the Calculator, and bring their centres coincident, and 
drive a pin through both ; turn Template till it takes posi- 
tion shown in Fig. 1. The small circle P., Fig. 1, denote?^ 
the Crank Pin, i of it occuring on Template. 



On Template at T, Fig. 1, coincident with thick line on 
Calculator, make small mark, now turn the Template round 
till the mark reaches the next verticle line, toward F, and 
the Valve has opened tlie Steam Port J^in. ; another reached 
and it is opened J io., and when the mark has got round 
to the line B. F. the port is open as much as it will open, 
and the Crank Pin has made half stroke, but tlie exact 
position of Piston in Cylinder will be found by counting 
the numDer of curved lines from either end of ''Stroke 
Circle," toward the Crank 1 'in. 

Moving the Template further round, the mark returns; 
and when the next line is reached the port is ^ in. closed, and 
when mark is again coincident with thick line, the. port is 
closed. • . " ' 

It will be evident b}" this time the thick line has been 
the receiving edge of Steam Port, and the mark the receiv- 
ing edge of valve; and since the valve had no lap, the 
Crank Pin is on the dead centre line B. F. 2Tow, we must 
assume the thick line to be the exiiaustixo or ixsiue edge 
of Steam Port, and the mark the exhausting or inside 
edge of Yalve. This being understood we proceed to turn 
Template round again, and when the first line on the B. 
side of thick line is reached, then the exhaust port is opened 
^ in., provided the valve has no inside lap, for if it had 
^ in. inside lap then the mark would just have reached the 
thick line or edge of port ; this would be bad, as we see 
the Crank Pin is already started on its way back ; but we 
shall say the Valve has no inside lap and proceed ; so the 
port is open ^ in. and when the mai^k shall reach the line 
B. F., the exhaust will be open as much as this travel of 
valve will allow, and when at thick line again, is closed, 
and engine has made one revolution. . The Crank Pin on 
the dead centre line, and mark at thick line, ready to 
leave it by the advance of the Crank Pin, and represent 
the action of taking steam as before. A Valve construct* 
ed thus would read: 



3 



Travel of Valve, - - 2 inches. 

Cutoff, - - - - " 

Exhausts from end of Stroke, - " 

Expands, - - _ " 

Cushions, - - - '' 

Lap, - - - " 

Steam Port opens, - 1 '' 

Exhaust Port opens, - - 1 " 

Lead, - - - " 

This was the kind of Valve in use for some time after 
the steam engine was invented, and even at this late day 
tell tale diagrams, taken up to date, show that the good 
effects of Lap is either not appreciated, or understood by 
some builders yet. 

It may not be amiss to say here, that the word Lap is 
often used when it would be more appropriate to say Cut 
off*; for instance we hear of a Valve having so much Lap, 
instead of at what part of the stroke the Lap cuts off the 
steam ; the first has no meaning, whereas the latter tells 
the economy aimed at, other things being equal. 

But of more importance even than this is the action of 
the exhaust. The same diagrams show fearful waste of 
steam in this direction also ; in fact there can be no other 
conclusion ; after examining many diagrams and valves 
off engines by different builders, both east and west, than 
that there is wide spread ignorance on this subject. Some 
builders give the same outside and inside lap on all occa- 
sions, no matter what the size of the engine, or travel of 
the valve. 

It ought to be understood that the result of inside lap 
is to exhaust too late and cushion too early ; occasioning 
back pressure all the way, and making bad worse by shut- 
ting off what small passage there is, before the piston is 
near the end of the stroke, and compressing what steam 
there is left in the cylinder, that had not time to get away, 
into less volume, increasing its pressure above the pressure 
in the steam chest, till it forces the valve off its seat and 



escapes into the steam chest among th^ live stea/n. Tt is 
this state of things which hinders the more general intro- 
duction of the Balanced Valve, because being balanced it 
takes LESS to lift it ; and ignorant builders gravely object 
to its use as being '' too sensitive." And it is thrown out ; 
thereby removing the effect instead of enquiring into the 
cause. 

In valves which cover the two steam ports and the mid or 
exhaust port at once, ( Three Port Valves,) if there is no 
inside lap the exhaust of one port may pass over the mid 
port and enter the other port, and under unfavorable cir- 
cumstances, produce back pressure, on the stroke just 
being completed. It was probably this fact which led 
many builders into the mistake of carrying out the same 
idea in Double Port Cylinders, when there is no neceesity 
for it. In fact it may safely be said, that there is no 
greater drawback to the average steam engine to-day, than 
this inside lap. It is this which makes some engines stop 
short of the dead centre and travel backward some distance 
without steam. It is this which causes the slide valve to 
jerk up off its seat as the piston nears the end of its stroke. 
It is this which causes some engines to make a great noise 
exhausting, because the Piston has to push the steam out 
of the Cylinder. 

It is here the improvement is made when one builder 
undertakes to make some other builder's engines, do 
'-'• double the work with half the fuel." 

By proper attention to this alone, and having the Valve 
set properly by the Indicator, more fuel can be saved than 
by all other late improvements put together. It is evident 
then that Three Port Valves ought to be discarded, and 
Double Valves take their place on all engines, unless they 
are so small that it can't possibly be done ; even this change 
on engines from 5 or 6 in. upward, would pay all parties 
for the steam wasted in the long ports each stroke, under 
ordinary circumstances, would run the engine two or three 



hours out of every ten, easy, to say nothing of the chance 
it gives to exhaust earlier and cushion less. 

EXAMPLE WITH LAP. 

In this example the term Lap will mean the usual lap 
given to each end of the Valve, when on the middle of 
its travel, and the term inside lap, ( used for w^ant of a 
better,) will mean the distance A. (in Fig. 2) when the 
valve is in the position shown, 




Fig. 2. 

And to make the case plainer, we will assume a given size 
of engine and ports, and state in advance what disposition 
of steam is desired in the Cjdinder. 

Engine, 12 in. diameter of cylinder x 24 in. stroke, ports 
equal to one-tenth area of cylinder, equal to 12 in. by 1|-, 
to cut off steam at f of the stroke, and to exhaust at 3 
inches from end of stroke, and for a trial we will adopt 2J 
in. travel of valve, the cushion being a result to be deter- 
mined. And to divest the " mark " of mystery, let us 
imagine it to be a mere wrist pin and a valve attached to 
it, and being draged along backward and forward by its 
movements. 

The crank pin is on the dead centre line B. F., and the 
valve has to be moved ahead to take up the lap and give 
steam when in that position. This is done by simply 
making a new mark on the template. Removed from the 
thick line, in the direction of F., the amount of the lap 
required. ^ If we had not known the amount of lap required 
we mighltTry f in., and if we found that would cut off too 
late, then J in., &c., but it happens that i plus A is the re- 
quired lap, and accordingly we make a mark on template 



6 



I plus A in. from thick line, measuring by the eye simply, 
as the upright lines stand ^ in. apart. If the template be 
turned now it will be found that the steam port is opened 
T6 in., and when the mark has arrived at the identical spot 
it started from, only on the under side of line B. F., it will 
be found that the crank pin stands at the f line, and the 
piston has proceeded two-thirds of its stroke; but the 
exact distance in inches can be found by counting the 
curved lines from F. back to crank pin. Counting with 
pencil or pointer along stroke circle, each space representing 
in this case 1 in. It will be found there are eight of them 
and eight inches is the distance piston is from end of stroke. 
Now the proper way to find the inside lap, is to move 
the mark round ^ in. at a time, and at each ^ in. stop and 
examine the position of the crank pin, to see if it is nearing 
the desired exhausting point. In this case ^ in. would 
bring the mark to within A of the fourth line from thick 
one, and the crank pin is some distance yet from 3d inch 
from end of stroke, ( the exhausting point,) showing that 
J in. is not enough inside lap. Another J in. and the mark 
is within A in. of third line, and still the crank pin is not 
at the desired place ; we try another and examine, and still 
another, making t in. in all, or i in., and the crank pin 
wants a little yet ; but by moving the mark A in. more, 
making I plus A in. inside lap, we find by counting as before 
the crank pin has arrived at 3 in. from end of stroke. 
JsTow it is evident that further movement of the mark will 
result in opening the exhaust, and when it has moved to 
line B. F., the exhaust will be full open, and when it 
arrives at the same line again, on top side of line B. F., 
the exhaust will be closed. This we proceed to do, but we 
may as well observe as we go along, how much said port is 
open when piston is at end of stroke, by proceeding as 
before, counting one J in. after another, we find six of them 
are passed before piston is. at end of stroke, showing that 
the exhaust is f in. open by the time crank pin is on dead 



centre line ; and further, we may as well see if exhaust port is 
going to be opened full or not. The mark was ^ in. from 
thick line when exhaust port began to open, and will be full 
open when mark is on line B. F, ; now the space interven- 
ing measures 1+ in., whereas the port is only 1^ in., conse- 
tjuently the valve tnivels, not (mly over the port, opening 
it full, but I in. more ; this is good as it wears the seat and 
valve uniform. I^ow by moving the mark round to the line 
corresponding with the opening of exhaust, viz : ^ in. from 
thick line — we find the crank pin stands at If in. from end ot 
stroke, as the curved lines show If in. then is the cushion. 
If it should be desired to have a little more cushion, we 
go back over the same ground and give more inside lap, 
but this amount, with slight lead, would run well at 300 or 
400 ft. piston speed. Lead would have the effect of opening 
the exhaust sooner and reducing the cushion ; but what 
was lost in cushion in this way, would be made up by the 
entering of the live steam before turning the centres, pro- 
ducing the same result, without the tendency to lift the 
valve oft* its seat. A note of results ought to be jotted 
down as they are found, and recorded in a book kept for 
the purpose when they are adopted. The results given by 
this valve would read as follows: 







BACK 


AND FSONT. 
B. 


F 


Travel of Val 


ve. 


^ 


2i inch. 


?i inch. 


Lap, 


- 


- 


1 pkis yV inch. 


1 plus 3^2 inch. 


Cutoff, - 




■ 


8 inch. 


10 inch. 


Inside Lap, 


- 


- 


^ pkis 3^2 ii^cii- 


i plus 3^2 inch. 


Exhausts at 




. 


3 inch. 


4 inch. 


Expands, 


- 


- 


5 inch. 


6 inch. 


Cusliions, 




. 


If inch. 


1^ inch. 


Steam ort opens 


- 


Y^g inch. 


y%inch. 


Exhaust open 


at end of Stroke, 


f inch. 


f inch. 


Exhaust Port 


opens 


- 


FuU plus i inch. 


Full plus i inch. 



B. column denotes back end of cylinder and F. column 
the front end, which is found in the same way, only the 
Calculator is turned so that letters B. F. will read up side 
down. To make the Value cut off and exhaust equal, we 



8 



must give different amounts of lap on each end of the 
Valve. This would occasion the opening of one port 
sooner than the other, and also the difference wider. The 
result would be as follows : 

B. F. 

Travel of Valve, - - 2|- incli. 2J incli. 

Lap, - - I plus J^ inch. | inch. 

Cut off, - _ 8 inch. 8 inch. 

Inside Lap, - . - ^ plus ^\ inch. i inch . 

Exhausts at - .3 inch. 3 inch. 

Cushions at - - If inch. 1^ inch. 

Steam Port opens, - - A inch. i inch. 

Expansion, - - 5 inch. 5 inch. 

* Lead, - . inch. jq inch. 

It will be seen that if a good thing is desired in one 
direction, it is at a sacrifice in another. But there are cir- 
cumstances where this Lead, necessary for equal cut off, is 
very advantageous. In engines for instance where large 
reciprocating ports move vertically, it is sometimes neces 
sary to go even further than this and make a distorted valve 
purposly, to accomplish certain ends. The duty of the 
Calculator is done however when it shows the disposition 
of the steam under different conditions. It remains with 
the designer to choose which suits him best, and cut the 
valve to do his will. 

If it is desired to see what effect lead obtained by 
moving the eccentric ahead will have, we proceed as 
before, but when the mark has moved forward the 
amount of lead required, move the template no ftirther 
until we have made a new mark on template, coincident 
with line B. P., to represent new relation of crank pin to 
mark ; and through the operation use this new crank pin 
in place of the old. 

By moving template back to old position, i. e., till old 
crank pin is on line B. F., the new crank pin will show 
just how far the piston is from end of stroke. This is of 
some importance and ought to be jotted down with the 

* The lead here mentioned is not the lead obtained by moving the 
eccentric ahead, but by cutting j\ in. off one end of the valve. 



others in case it be called in question. The record book 
will be found to be a good investment, if a reliable man is 
sent out to fit up the engines and sets the valve not '' in 
the neighborhood of" but exactly as it is designed to be 
set. Paper templates ought to be made of valve and seat, 
and the ( paper ) valve moved along the ( paper ) seat, and 
seat trimmed off so that valve will move over every edge 
J in., for this purpose the exhaust port ought to be J in. 
wider than steam port. More can't hurt if valve is balanced. 
A good plan to have seat and valve chipped and planed 
correct, is to prepare a stick with seats marked on one edge 
and valve on another, and these handed to the fitter to 
chip seats to. These sticks ought to be '' laid off" very cor- 
rectly ; the lines drawn deep with a pen knife, and a small 
chamfer taken off one side of each line ; and the space 
corresponding with ports varnished black, and the rest of 
the stick varnished yellow. It is not the design of these 
pages to discuss the size of steam ports, but I have frequently 
met young engineers discouraged by the great disparity of 
rules given by different writers. An examination of seven 
popular Avorks, reveals the fact that the rules, by application, 
give results varying 45 per cent. For example, an engine 
28 inches diameter of cylinder, by 48 inches stroke, making 
60 revolutions, requires by one rule 41 square inches of 
steam port, while another calls for 76. The others more or 
less between these figures, the mean of all being 61. Aside 
from rules of this kind, the Indicator has done much 
towards establishing the proper size of ports. By its use 
TO the area of Cylinder's diameter is found to answer very 
well for the ordinary Slide Valve engines and piston speeds 
of to-day ; and perhaps the explanation of the disparity 
refered to is to be found in the difference in the dates of 
publication ; for not only has piston speed but steam pres- 
sure been on the increase for a number of years, the 
former from 250 to 600, the latter from 20 to 140. Although 
these high pressures and high speeds are not yet popular. 



10 



The next leap of economy in the steam engine will proba- 
bly come in this direction ; for with reciprocating ports 
well proportioned and counterbalanced, and slide valve 
properly balanced also, much will be gained by increased 
speed, other things being equal. 

It is almost superfluous to add, that in the case of an 
old valve, we proceed in the same manner as in preceeding 
examples, only, in this case, the travel of valve, and lap 
and inside lap are known ; and by making ( paper) valve 
and seat, and moving them back and forth, equal the 
travel, we see whether the various edges pass over each 
other properly, and whether the dimensions of exhaust 
ports are encroached upon by movement of the valve in 
working. And by the Calculator we can see what eftect 
more or less lap, or inside lap, will have, or more or less 
travel, in case its doings should be found to be unsatisfactory. 



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